MOS (metal oxide semiconductor) power transistors or MOS power devices which are commonly employed in automotive and industrial electronics, should have a low on-state resistance (Ron) when being switched on. In an off-state, they should have a high breakdown voltage characteristic and withstand high source-drain voltages. For example, a MOS power transistor should withstand a drain-source voltage Vds of some tens to some hundreds or even thousand volts when being switched off. As a further example, MOS power transistors conduct a very large current which may be up to some hundreds of amperes when a gate-source voltage of about 2 to 20 V is applied, and at a low voltage drop Vds.
In a lateral power device a current flow mainly is effected in a direction parallel to a first main surface of a semiconductor substrate. Generally, in power devices a predetermined thickness of the isolation layer that is disposed between the field plate and the silicon drift region improves the on-current at a certain breakdown voltage characteristic.
Attempts are being made in order to improve the isolation layer between the field plate and the drift region.